Fig.3-3 show the C-V characteristics of the single high-κ HfO2 layer MIS capacitors processed by PDA at 600oC flowed in N2 ambient. We apply voltage on MoN electrode and erase the high-κ HfO2 /Si MIS capacitors from -13V to 13 Volt, and program the high-κ HfO2-ZrO2/Si MIS capacitors from 13V to -13 V, and it just has 3.5V memory window. the holes tunnel in HfO2 layer to recombine electrons and eliminate the VFB in erase operation, On the contrary, the electrons tunnel in HfO2 layer and VFB elevate. The value of capacitance density is 9.3 fF/μm2, we can calculate the κ value is 19. There are three kind of leakage mechanism. MoN metal Gate has large work function so that electron will suffer a high barrier when the external voltage is small. In this way, electrons can not transport to dielectric film, called Schottky Emission. We can use following equation to represent.
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⎥⎦ Poole-Frenkel Effect, it means there have charges be trapped in dielectric layer. The Poole-Frenkel effect is the lowering of a Coulombic potential barrier when it interacts with an electric field, and is usually associated with the lowering of a trap barrier in the bulk of an insulator, as shown in Fig.3-4. We can use following equation to represent.
⎥⎦ If the external bias is big enough, F-N tunneling will decide the leakage m . We can draw ln(J)-E1/2 and ln(J/T2)-E1/2 relation, and calculate the value of b
echanism
ν is -0.78 (the intercept of y-axis in Fig.3-5(b) multiplied kT ), knowing that the charges was not catch to deep level. To measure retention, I triggered a constant voltage of +10V for program during the pulse length of 1s to the MoN electrode, then, I measured the C-V curves and extracted VFB shift pass through times. Repeat the same action for erase, the VFB became larger. Figs.3-6(a) and (b) show poor retention for HfO2 single layer, therefore, improving the trapping layer by interactive structure.
HfO2 and ZrO2 these two materials can’t endure temperature more than 35OC when programming process. If depositing them by E-Gun system, temperature is hard to control and the dielectric film may be destroyed. Therefore, I deposit them by sputter system.
Due to the κ value of Hafnium oxide (HfO2) is 25 and Zirconium oxide (ZrO2) is
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35, we can elementarily count up ideal capacitance density. In Eq.3-5, is permittivity, A is the capacitor area and t is the thickness of capacitor.
(Eq.3-5) Calculation of ideal capacitance density of interactive structure in the following equations:
(Eq.3-6)
= (Eq.3-7)
(Eq.3-8) By Eqs.3-6 and 3-7, EOT is 2.4nm for MIS which mix up Zirconium oxide (ZrO2)
to Hafnium oxide (HfO2), it is obviously increasing the EOT.
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Figs.3-7 and 3-8 show the measured C-V hysteresis of interactive dielectric MoN/HfO2-ZrO2/Si capacitors measuring by HP4284. We apply voltage on MoN electrode and erase the high-κ HfO2-ZrO2/Si MIS capacitors from -13V to 13 Volt, and and program the high-κ HfO2-ZrO2/Si MIS capacitors from 13V to -13 V. It shows large memory window character of 4.7V and the value of capacitance density is 12.2 fF/μm2 whose dielectric is post-deposition annealed in O2 ambient at 600oC for 5 min. The interactive dielectric HfO2-ZrO2 after post-deposition annealed in N2 ambient at 600oC for 5 min shows 4.3V memory window and the value of of capacitance density is 11.5 fF/μm2. The value of capacitance density elevates.
Memory window increasing may be due to increasing charges trapped in dielectric. Single layer has small memory window, the recipes of going through PDA at 600oC flowed N2 ambient just exhibit 3.5V P/E shift by contrast. Double-layer
Double-layer structure lattice was recombined by PDA process and two high-κ materials could be mix together. Although HfO2 and ZrO2 have similar band-gap and band-diagram, ZrO2 in HfO2 increase the κ value (the κ value of ZrO2 and HfO2 is 35 and 25 respectively) and decrease effective oxide thickness. The high capacitor density density is especially important for backend capacitor due to the very thick equivalent-oxide thickness (EOT) > 5 nm and hence the low leakage current. On the other hand, low leakage current is one of the most important factors for high-κ gate dielectric with typical EOT ≤2 nm[3.10]-[3.16].
Fig.3-9 shows the schematic band diagram of metal-gate/HfO2-ZrO2/Si capacitor.
The possible erase mechanism may arise from the smaller bandgap (EG ~6.0 eV), small bandgap has more probabilities to catch electrons. This could permit hole injection or electron tunneling out from the high density of trap states, electrons tunnel from Si-sub to trapping layer when metal gate applied positive bias, and hole injection recombines electron trapped deeply in dielectric as metal applied negative bias (Fig.3-10).
In Fig.3-11(b), the value of νb PDA in O2 ambient at 600oC for 5 min in Poole-Frenkel Effect is -0.971, and the value of νb PDA in N2 ambient at 600oC for 5 min in Poole-Frenkel Effect is -0.931 calculated by intercept of Fig.3-12(b) multiply to the value of kT. Compare modulus of νb
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, PDA in O2
ambient has excellent ability to catch charges in deep position of trapping layer.
In addition to trapping position, retention is one of the important issue for discuss interactive HfO2-ZrO2 layer. On the whole, a device revealing good retention should have slow velocity to P/E. Figs. 3-13 and 3-14 exhibit the research of interactive HfO2-ZrO2. It says that processed PDA in O2 ambient at 600oC for 5 min shows shows good retention for ten years and has excellent speed in erase
operation. PDA in N2 ambient at 600oC for 5 min revealed inferior retention for ten years and the P/E speed is slow because saturation need more time.
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Fig.3-1 Cross section view of novel program-erasable interactive structure high-κ HfO2-ZrO2 MIS capacitors.
Fig.3-2 Cross section view of novel program-erasable high-κ HfO2 MIS capacitors.
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Fig.3-3 The measured C-V hysteresis of high-κ HfO2 MIS capacitors after Post-deposition annealing (PDA) in N2
ambient at 600oC for 5 min.
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Fig.3-4 Mechanism of Poole-Frenkel effect. The solid line represents the Coulombic barrier without a field. The dashed line shows the effect of an electric field on the barrier. The slope of the dash-dot line is proportional to the applied field.
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(a)
0 500 1000 1500 2000 2500 -20
0 500 1000 1500 2000 2500 -32
J-V of a MoN/HfO2/Si MIS device, where the electron injection is from the Si.(a) Calculated data using Schottky Emission (SE) and (b) Frenkel-Poole (FP) conduction models are included.30
(a)
Fig.3-6 (a) The retention characteristics of VFB from the C-V curves programmed or erased at +10V or -10 V,(b) The P/E characteristics for HfO2 MIS capacitor.
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Fig.3-7 The measured C-V hysteresis of interactive structure high-κ HfO2-ZrO2 MIS capacitors after Post-deposition annealing (PDA) in O2 ambient at 600oC for 5 min.
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Fig.3-8 The measured C-V hysteresis of interactive structure high-κ HfO2-ZrO2 MIS capacitors after Post-deposition annealing (PDA) in N2 ambient at 600oC for 5 min.
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Fig.3-9 The schematic band diagram of the MoN metal gate/high-κ HfO2-ZrO2/Si MIS capacitor.
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Fig.3-10 The schematic band diagram of the metal-gate/high-κ dielectric/Si MIS capacitor in erase state.
35
(a)
0 500 1000 1500 2000 2500 -20
0 500 1000 1500 2000 2500 -36
measured J-V of a MoN/HfO2-ZrO2/Si MIS processed PDA in O2 ambient at 600oC for 5 min, where the electron injection is from the Si.(a) Calculated data using Schottky Emission (SE) and (b) Frenkel-Poole (FP) conduction models are included.36
(a)
0 500 1000 1500 2000 2500 -20
0 500 1000 1500 2000 2500 -36
measured J-V of a MoN/HfO2-ZrO2/Si MIS processed PDA in N2 ambient at 600oC for 5 min, where the electron injection is from the Si.(a) Calculated data using Schottky Emission (SE) and (b) Frenkel-Poole (FP) conduction models are included.37
(a)
Fig.3-13 (a) The retention characteristics of VFB from the C-V curves programmed or erased at +10V or -10 V (b) The P/E characteristics of MoN/HfO2-ZrO2/Si MIS processed PDA in O2 ambient at 600oC for 5 min.
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(a)
Fig.3-14 (a) The retention characteristics of VFB from the C-V curves programmed or erased at +10V or -10 V (b) The P/E characteristics of MoN/HfO2-ZrO2/Si MIS processed PDA in N2 ambient at 600oC for 5 min.
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